Molecular characterization of a carboxy-terminal eukaryotic-cell-binding domain of intimin from enteropathogenic Escherichia coli.

A eukaryotic cell-binding domain from the intimin (Int) polypeptide of enteropathogenic Escherichia coli O127 (EPEC) was investigated. Derivatives of the carboxy-terminal 280-amino-acid domains of Int (Int-EPEC280) and the Int homolog invasin (Inv) from Yersinia pseudotuberculosis (InvYP280) were fused to the E. coli maltose-binding protein (MBP), expressed, and purified. The smallest MBP-IntEPEC fusion protein that efficiently mediated binding to HEp-2 cells, monitored by using purified fusion proteins in fluorescence activated cell sorter analysis or by using fluorescent Covaspheres coated with purified fusions, contained the carboxy-terminal 150 amino acids of Int. Replacement of Cys-937 with Ser (IntEPEC280CS) destroyed the cell-binding activity of IntEPEC280. Covaspheres coated with MBP-IntEPEC280 were associated with HEp-2 cell microvilli but failed to induce actin accumulation underneath bound particles or cell spreading on coated plastic surfaces. MBP-IntEPEC280, but not MBP, MBP-IntEPEC280CS, or MBP-InvYP280, inhibited EPEC entry into HEp-2 cells.